Metal strip is normally produced in a continuous process involving extrusion and/or rolling. The strip produced in this manner normally must undergo a leveling process whereby its is rendered planer. With thin metal strip of aluminum alloy, this is typically done as the strip is advanced in its longitudinal travel direction by plastically deforming it in one or in several stretch-leveling zones under a tension generally at or above the stretch limit. Thin metal strip signifies in particular metal strip with a thickness of 0.05 to 1 mm, preferably 0.1 to 0.5 mm. The stretch-leveling zone usually is that region of the strip in a strip treatment installation between two driven rolls where the strip is plastically lengthened and maintained under a tension about equal to the stretch limit.
With continuous stretch-leveling the strip runs through an upstream set of braking rolls and a downstream set of traction rolls and is subjected to stretch leveling between the two sets of rolls as a result of being plastically stretched. The strip can run through several such stretch zones between respective sets of rolls and be stretched in each these stretch zones in the plastic range and/or in the elastic range (see U.S. Pat. No. 7,013,693).
In addition to stretch leveling, the leveling of metal strip can also be done by rolls, e.g. by dressing rolls and/or by leveling. In practice, corrugations or strip saber cannot be completely eliminated with the known methods of leveling metal strip by rolls, leveling and/or stretch leveling, so that a perfectly level condition is rarely achieved.
For this reason it has been suggested, especially during rolling, that a temperature profile that can be varied over the strip width and optionally over a given strip length be created in the metal strip by heating or cooling locally in order to influence the distribution of the tensile stress. The degree of leveling is consequently adjusted in this case by varying the distribution of the tensile stress (see U.S. Pat. No. 6,327,883).